The Hepatitis B virus (HBV) is an enveloped, partially double-stranded DNA (dsDNA) virus of the Hepadnavirus family (Hepadnaviridae). Its genome contains 4 overlapping reading frames: the precore/core gene; the polymerase gene; the L, M, and S genes, which encode for the 3 envelope proteins; and the X gene.
Upon infection, the partially double-stranded DNA genome (the relaxed circular DNA; rcDNA) is converted to a covalently closed circular DNA (cccDNA) in the nucleus of the host cell and the viral mRNAs are transcribed. Once encapsidated, the pregenomic RNA (pgRNA), which also codes for core protein and Pol, serves as the template for reverse transcription, which regenerates the partially dsDNA genome (rcDNA) in the nucleocapsid.
HBV has caused epidemics in parts of Asia and Africa, and it is endemic in China.
HBV has infected approximately 2 billion people worldwide of which approximately 350 million people have developed chronic infections. The virus causes the disease hepatitis B and chronic infection is correlated with a strongly increased risk for the development cirrhosis and hepatocellular carcinoma.
Transmission of hepatitis B virus results from exposure to infectious blood or body fluids, while viral DNA has been detected in the saliva, tears, and urine of chronic carriers with high titer DNA in serum.
An effective and well-tolerated vaccine exists, but direct treatment options are currently limited to interferon and the following antivirals; tenofovir, lamivudine, adefovir, entecavir and telbivudine. Interferon is expensive and frequently not well tolerated, and nucleosides have been shown to select for resistant mutants.
Drug screens have identified heteroaryldihydropyrimidines (HAPs) as a class of HBV inhibitors in tissue culture and animal models, effective at nanomolar concentrations (Weber et al., Antiviral Res. 54: 69-78). Further research has shown that HAPs target Cp (Deres et al., Science 299: 893-896), causing the inappropriate assembly of capsid at higher drug concentrations.
A number of patents and patent applications disclose compounds with HBV inhibitory activity, in particular dihydropyrimidine derivatives, including WO00/058302, WO01/68642 and WO2010/069147.
Amongst the problems which HBV direct antivirals may encounter are toxicity, mutagenicity, lack of selectivity, poor efficacy, poor bioavailability, racemisation of chiral centers and difficulty of synthesis.
There is a need for HBV inhibitors that may overcome at least one of these disadvantages.